lecture 12

what are dental ceramics

inorganic compounds with non-metallic properties

typically consist of oxygen and 1 or more metallic/non-metallic elements

elements can be

aluminium

calcium

lithium

magnesium

potassium

silicon

sodium

tin

titanium

zirconium

what is the ceramic fit provided for veneering usually composed of

mixture of glass and crystalline structures

what is porcelain

relatively dense, white ceramic material produced by sintering a mixture of feldspar, kaolin, quartz and other substances - have to have kaolin in tho

when was the first porcelain material introduced and by who

1789 by De Chemant and Duchateau

who introduced platinum foil and pins for fixing

fonzi in 1808

who established the first commerical production and founded the SS White company

stockton in 1825

what was the SS White company

the first porcelain tooth manufacturing company

who placed the first ceramic crown on platinum foil

charles land in 1903

who published the first dental monograph in bulgaria on dental ceramics

Dimitar Svrakov in 1940

what do

sintering

fritting

glass ceramic

poly-crystalline ceramic mean

SINTERING

a process where individual particles bond by atomic or molecular diffusion. they form a monolithic solid

FRITTING

a process where constituent components are melted into a glass then cooled into water. made when water soluble particles present.

GLASS CERAMIC

ceramic material consist of at least one glassy and one crystalline phase produced by controlled glass crystallisation

POLY CRYSTALLINE CERAMIC

ceramic material consisting of several crystalline phases. does not contain a glassy phase

what are

CAD/CAM ceramics

Casting ceramics

Pressable ceramics

Feldspathic ceramics

CAD/CAM CERAMICS

ceramic materials used to produce a partial or complete ceramic prosthetic structure using tech

CASTING CERAMICS

material specifically designed to be cast in refractory sockets for a ceramic crown or bridge

PRESSABLE CERAMICS

material heated to a temp that is fluid and pressed by isostatic pressure into a specific refractory shape

FELDSPATHIC PROCELAIN

ceramic material consisting of a glass matrix and 1 or more crystalline phases

eg leucite (KAlSi2O6) and apatite [9Ca5(PO)43(F.Cl.OH)]

what is a spinel and what is a ceramic glaze

spinel is a material consisting of mixed oxides like MgO.Al2O3

ceramic glazes form a perfect, smooth, glossy surface

process is

formulated ceramic powder mixed with liquid

applied to ceramic surface

heated at suitable temp for specific time

what are ceramic stains (colour modifiers),

devitrification,

transformation toughening

ceramic stains are a mixture of 1 or more metal oxides and low melting glass.

it modifies colour of ceramic restoration

devitrification is a change in amorphous porcelains where crystalline areas are formed within phase

transformation toughening is a ceramic strengthening mechanism that occurs thru transformation of crystalline structures.

eg:

stress-activated tetragonal to monoclinic transformation in yttria stabilised zirconia.

classification based on usage

according to Kissov

group 1

ceramic materials for reinforcement of veneering porcelains

group 2

veneering ceramic materials

group 3

porcelains for fabrication of artificial teeth

classification according to sintering and temp

HIGH FUSING

1300 deg

artificial teeth

substructure in ceramic-ceramic systems

MEDIUM FUSING

1101-1300 deg

artificial teeth

presintered zirconia

LOW FUSING

850-1100 deg

crown and bridge veneer ceramic

ULTRALOW FUSING

<850 deg

crown and bridge veneer ceramic

classification according to phase composition

glass matric ceramic

- feldspathic

- synthetic

- glass infiltrated

poycrystalline ceramic

- alumina

- stabilised zirconia

- zirconia toughened alumina

- alumina toughened zirconia

resin-matrix ceramic

- resin nanoceramic

- glass ceramic in resin interpenetrating matrix

- zirconia-silica ceramic in a resin interpenetrating matrix

properties of ceramic materials

chemical properties

chemical inert materials

stable surface of restorations

do not emit harmful products

resistant to corrosion

dissolve on application of fluorides

eg 1.23% fluoride gel for caries prevention. keep for 40 mins

properties of ceramic materials

mechanical properties

possess good to excellent compressive strength

good to excellent flexural fracture toughness

zirconia based ceramics are with highest flexural strength - similar to steel but fracture toughness is lower than steel

brittle

tensile strength is not a great indicator of resistance

properties of ceramic materials

abrasiveness

a form of fracture that takes place on microscopic level.

greater hardness difference, greater abrasion

properties of ceramic materials

abrasion mechanisms

1. asperities on ceramic surface create high level of stress --> microcracks

2. wear as a result of high stress and large difference in hardness between 2 surfaces

3. impact or erosion due to abrasive particles dissolved in a liquid.

microcracks due to high point pressure

properties of ceramic materials

abrasion factors

properties of ceramics

factors of oral environment. -

eg flourine compounds,

carbonated beverages,

mode of mastication

contact surfaces

wetting by saliva

contact time with abrasive particles

properties of ceramic materials

biological

biocompatible material due to inertness and corrosion resistance

lead separation up to 250 ppm in feldspathic porcelains

ISO 6872 - 4% acetic acid at 80 deg for 16h

properties of ceramic materials

physical

colour + ability to transmit colour

- value

- hue

- chroma

- translucency

- effects

zone of translucency

law of energy conservation: Ki+Ui=Kf+Uf. U is potential energy and K is kinetic energy.

E-incident = E-diffused +E-reflected +E-absorbed +E-transmitted +E-fluoresced

pigment colouring

- selective absorption

- selective reflection

thermal conductivity

electrical conductivity

all ceramic systems

main reasons for inc use:

development of CAD/CAM

development of polycrystalline ceramics with enhanced mechanical and aesthetic performance

development of materials for pressed ceramic tech

methods for inc strength of ceramics

changing microstructure

reducing stressing via manufacturing tech and restoration design

changing microstructure (methods of inc strength of ceramics)

thermal tempering

localised compressive stresses are created on rapid cooling

outer layer cooled first

underlying layers compressed

before ion exchange (methods of inc strength of ceramics)

creates compressive forces in surface layer of ceramic

feldspathic porcelain with sodium ions on surface

bath with molten potassium nitrate

after cooling, potassium ions replace smaller sodium ions

after ion exchange (methods of inc strength of ceramics)

diameter of K > Na by 35%

creates a cluster of atoms

inc bending strength by over 100%

works at depths up to 100µm

can be lost by machining, abrasion, impact of inorganic acids

limiting crack propagation (methods of inc strength of ceramics)

dispersion of the crystalline phase

microcracks propagate more readily in vitreous phase

confined on reaching crystal

inc in microcrystals dispersed in vitreous phase inc fracture toughness

transformation toughness is the ability of a material to undergo stress induced transformation in crystal structure that limits the development of cracks

eg tetragonal zirconia crystals into a stable monoclinic form that limits cracks

choice of dental ceramics

survivability - material composition, fabrication technique, bonding method

eg zirconia based are good

success rate - influenced by oral health habit of patient, material used and restoration material quality

aesthetic effect - natural translucency, colour matching

eg: feldspathic materials and lithium disilicate

allergenic potentials (metals) - metal free options like zirconia can be alternatives

biologically oriented prep - those with adhesive bonding capabilities and provide long lasting aesthetic restorations

what are feldspar porcelain, aluminium porcelain and leucite glass ceramic used for

FELDSPAR

primary = veneers

secondary = partial crowns

contraindications = inlay, onlay, crowns an bridges, parafunctions

ALUMINIUM PORCELAIN

primary = ceramic framework

secondary = crowns on premolar

contraindications = crown on molars, bridges, parafunctions

LEUCITE GLASS

primary = anterior single crowns and veneers

secondary = crown on premolar

contraindications = restoration subjected to high masticatory load

bridges and parafunctions

what are aluminium ceramic infiltrated with glass, zirconia infiltrated with glass and zirconia (Y-TZP) with veneering porcelain used for

ALUMINIUM ....

primary = ant and post single crowns

secondary = framework for ant FPDs up to 3 units

contraindications = ant veneers and crowns where high translucency is required, parafunctions

ZIRCONIA....

primary = distal crowns

post bridges up to 3 units

secondary = framework for ant FDPs up to 3 units

contraindications = ant veneers and crowns where high translucency is required, parafunctions

ZIRCONIA (Y-TZP)

primary = distal crowns and bridges up to 5 units

secondary = xxxx

contraindications = ant veneers and crowns where high translucency is required, parafunctions

what are zirconias:

3Y-TZP

4Y-PSZ

5Y-PSZ used for

3Y-TZP

primary = post crowns and bridges

secondary = framework for distal restorations

contraindications = ant veneers and crowns where high translucency is required, parafunctions

4Y-PSZ

primary = ant and post crowns, veneers and onlays

secondary = xxxx

contraindications = bridges, high stress areas, parafunctions

5Y-PSZ

primary = ant and post crowns, veneers, onlays

secondary = xxxx

contraindications = bridges, high stress areas, parafunctions.

factors determining the survival of distal restorations

strength and fracture toughness

size of retainer/pontic connection

retainer/pontic connection shape (embrasures)

patient specific masticatory force